We find that Ag-interstitial (AgI) acts as an electron donor and plays an important role in Ag-excess doped polycrystalline PbTe thermoelectric materials. When Ag is heavily doped in PbTe, the neutral (Ag-Ag) dimer defect is formed at the Pb-site and the environment becomes Pb-rich/Te-poor condition. Then the positively ionized Ag interstitial (AgI+) defect becomes the major defect under Pb-rich condition. Due to the small formation energy and small diffusion barrier of AgI+, Ag can be easily dissolved into the PbTe matrix. The temperature behavior of the Ag defect formation energy well explains the AgI+ solubility, the electron carrier generation, and the increasing electrical conductivity in Ag-excess doped polycrystalline PbTe at high temperature. This abnormal doping behavior by forming interstitial defects is also found for Au-doped PbTe.
@article{arxiv.1506.01584,
title = {Defects responsible for abnormal n-type conductivity in Ag-excess doped PbTe thermoelectrics},
author = {Byungki Ryu and Min-Wook Oh and Jae Ki Lee and Ji Eun Lee and Sung-Jae Joo and Bong-Seo Kim and Bog-Ki Min and Hee-Woong Lee and Su-Dong Park},
journal= {arXiv preprint arXiv:1506.01584},
year = {2015}
}